Flow stoppage indicator for mill fuel supply



1955 w. GREACEN, 3RD., ETAL 2,698,929

now STOPPAGE INDICATOR FOR MILL, FUEL SUPPLY Filed Jan. 25, 1952 Senifivity Fuel Hoppgr 22 Ad uster M Signcl Mlcrophone 6 b current 2Impulse Recfifier h HOW x 1 PSuchor 3 Diaahm Ampllfler Fllier Power FuelSource @311 5 0| d 8/ 5 "y Sen sifivity To Burners AS Q1 23: Ad uster45\ g 53 Alarm Oircuii 20 Flow 5 3% Aftion Exhouster A a Fan Swizz]: II: A SW 5 Walter Greacen 3rd Alexander Bogoi BY Harry A. Bishop ATTbRNUnited States PatentO FLOW STOPPAGE INDICATOR FOR MILL FUEL SUPPLYApplication January 25, 1952, Serial No. 268,266

4 Claims. or. 340-239 This invention relates to indicating possiblestoppages in the flow of fuel or other material to pulverizing mills,and it has particular reference to improved means for activating alarmapparatus in response to stoppage in the flow of coal to pulverizingmills such as supply the burners of boiler furnaces in steam powerplants.

Broadly stated, the object of this invention is to extend the usefulnessof no-flow alarm devices of the character here considered.

Another object is to better the performance and raise the reliability offlow indicator apparatus suitable for service with the coal feeders ofpulverizing mills of the air-swept type in the interiors of whichappreciable suction normally is maintained.

An additional object is to make novel use of the aforesaid suction indetecting stoppage of coal flow through the feed tube that leads intothe grinding chamber of the mill.

A further object is to supplement the new suctionactuated alarmapparatus for the feed tube by other alarm apparatus for the fuel feederserving said tube, and thereby provide a combination system whichafiords benefits and safeguards not obtainable heretofore.

Still further objects and advantages will become apparent from thefollowing description of illustrative embodiments of the invention whentaken in conjunction with the accompanying drawings wherein:

Fig. l is a representation partly in section and partly diagrammatic ofa conventional pulverizing mill and associated fuel feeder equipped withflow-indicator apparatus which incorporates the improvements of thisinvention; and

Fig. 2 shows how the Fig. 1 system may be modified to provide alarmcircuit activation directly by the suction switch without any timedelay.

The pulverizing mill to be benefited Illustrative of the variouspulverizing mills with which the improved no-flow alarm facilities ofthis invention may be used is the bowl type mill here shown ascomprising a base 1 supporting thereabove a casing 23 within the lowerportion 2 of which is a bowl 4 mounted on a vertical shaft 5 forrotation therewith. This vertical shaft is carried by bearings (notshown) mounted within the base 1 along with suitable gearing (likewisenot shown) through which the shaft 5 is rotated by a driving motor 6, ahorizontal shaft 7 being included in the driving connection.

A central feed tube 8 delivers the coal or other material to be grounddownwardly from a feeder 10 through the top of upper casing 3 and thenceinto the interior of bowl 4. As the bowl rotates centrifugal forcecarries the fuel outwardly to the upturned bowl rim causing passagebetween it and cooperating rollers 11, of which the representedapparatus has three (only one can be seen in Fig. 1). Each of theserollers 11 freely rotates about the lower end of a shaft 12 carried byarm 13 in rocker bearings 14, and is urged towards the rim of bowl 4 bya spring 15. The resulting force exerted upon the fuel passing betweenthe bowl rim and rollers serves to pulverize same and reduce theparticle size thereof.

' The-mill further is provided with an exhauster fan 16 organized todraw a current of air upwardly through themill casings 2 and 3, and hereshown as being driven by motor-,6 through shaft 7. This air comes into.the

2,698,929 Patented Jan. 4, 1955 lower part of casing 2 through an intakeconduit 17 and flows upwardly between the rim of bowl 4 and the casingwall, thereby carrying the sufficiently ground fuel up through casing 3and out top ontake 19 into suction conduit 20 and thence through fan 16to a discharge conduit 24 which may serve the burners of a boilerfurnace (not shown) in well known manner.

Within the upper'mill casing 3 there is provided classifier apparatuswhich serves in conventional manner to separate insufliciently groundmaterial out of the upflowing air stream and to return that separatedmaterial back into the interior of bowl 4 for re-grinding betweenrollers 11 and the bowl rim. Since such classifier apparatus is wellknown, no attempt has been made to show same here.

During operation of a pulverizing mill such as the one here illustratedand described, the interior of suction conduit 20 is maintained underappreciable negative pressure (which in practice may be of the order of6 inches water column) by the earlier explained action of exhauster fan16; and the space inside of upper mill casing 3 is by the same fanaction likewise kept under a negative pressure of only slightly lesserintensity, such, for example, as of 5 inches of water column. This meansthat as long as the mill continues to operate in normal manner thepressure inside of casing 3 and 2 will continuously be appreciably less(such as 5 inches water column) than the atmospheric pressure outside ofthe mill.

Since central feed tube 8 opens at its lower end 8a directly into millcasing 3, the aforesaid negative pressure also will exist inside of saidtube 8 unless clogging thereof occurs. Normally fuel passed by feeder 10from hopper 22 through slowly rotating star wheel 23 downwardly into thetop of central feed tube 8 drops freely through that tube and leaves atleast some open space through which the negative pressure impressed uponthe tube bottom 8a is freely communicated to the entire tube length; therepresented feeder 10 (including star wheel 23 and fuel-filled hopper22) constituting what amounts to a seal against admission of air intothe feed tube top 8b.

But restrictions of this central feed 8 sometimes do occur under certainconditions; such, for example, as when the material fed therethroughinto the mill is very wet or otherwise has a tendency to stick to thesides of the pipe building up to a point where the material flow may becut off either partially or even completely.

New alarm facilities depend on mill suction The new alarm facilities nowto be described are effective to detect plugging of this central feedtube 8 anywhere along its length from the lower end 8a opening into themill interior to the top portion 8b communicating with the fuel feeder10.

Said facilities utilize a diaphragm 25 enclosed on one side in an airtight casing 26 the interior of which communicates with the interior ofthe mill feed tube 8 through tubing 27 joined with said feed tube nearits top 8b. The other side of this diaphragm is exposed to theatmosphere, and from the diaphragm center there extends a rod 28 leadingto a switch 29 which occupies the open position shown as long as normalmill suction acts upon the diaphragm, but which is pulled into theclosed position by a spring 30 whenever the-suction within casing 26falls substantially below a given value selected by adjuster 31.

Other forms and organizations of suction-actuated switch apparatusobviously may be substituted for the illustrative devices here shown anddescribed.

In the arrangement shown by Fig. 1 the suction switch represented at 29controls a delayed action alarm switch AS associated with any suitableenergizing source here shown in the form of conductors 36-37.. Thewinding of switch AS is connected to receive from this source energizingcurrent when and only when suction switch 29 closes its contacts. Henceas long as fuel is dropping through mill feed tube 8 in normal manneralarm switch AS will be deenergized, in which event its contact 48 willoccupy the released position shown.

Controlled by said contact 48 is an alarm circuit.45-46.

ice

3 Under the condition stated in preceding paragraph, this alarm circuitcan receive no energizing current from power source 3637 over the AScontact point 49, and it is therefore maintained inactive.

Said normally released contact 48 of switch AS may have a desired pickup delay imparted thereto in any suitable manner as through the mediumof adjuster means represented at 50. Such means may take any one of anumber of well known forms such as a dash pot, clock work, electricalstorage mechanism or the like. As such devices are all conventional,detailed representation thereof has not been attempted; instead it willsufiice to say that in the illustrative arrangement shown adjuster 50may satisfactorily be chosen to provide for contact 48 a closure delayselectable anywhere within the range of from to 60 seconds.

Preferably, moreover, the mechanism 50 is so arranged that contact 48 ofswitch AS is free to move from the closed (horizontal) to the released(open) position without substantial retardation or delay. Assuming thatdevice 50 is set for a pickup delay of seconds, this means thatinterruptions in suction transmission to tubing 27 for less than 20seconds will be ineffective for causing switch AS to activate the alarmcircuit 45-46. With such setting the plugging of mill feed tube 8 mustcause suction switch 29 to close its contacts for more than 20 secondsbefore alarm switch AS can move contact 48 upwardly into engagement withpoint 49 and thereby connect the alarm circuit 4546 with its powersource 36-37.

Said alarm circuit may when so energized be arranged to light a signallamp 52, or to sound a bell 53 or a warning horn, or to accomplish anyother functions that may be desired in the particular installation. Oncesuch alarm warns the operator he may manually shut down the mill orinitiate other appropriate corrective actions, or automatic means (notshown) likewise may be activated in response to the detected plugging ofthe mill feed tube 8.

Operation of suction-responsive alarm system The manner in which the newsuction-responsive alarm system operates will have become more or lessapparent from the foregoing description of the component parts includedtherein. As long as the mill feed tube 8 remains unobstructed thesuction maintained by exhauster fan 16 within mill casing 3 iscommunicated through feed tube 8 and tubing 27 to chamber 26 and theupper side of diaphragm 25. Said suction pulls the diaphragm center upovercoming the tension of spring 30 and keeping the contacts of switch29 in the open position shown. Under this condition alarm switch AS isde-energized so that contact 48 thereof keeps the alarm circuitdisconnected from power source 3637.

Coal freely falling downwardly from feeder 10 through central tube 8into the pulverizing mill does not disturb the aforesaid communicationof the mill suction to diaphragm 25, and the alarm circuit 45-46 is inconsequence kept inactive under this condition of normal mill operation.But should for any reason the feed tube 8 become clogged or filled upwith fuel at any point between lower end 8a and the upper-end junctionwith tubing 27, such clogging will cut off communication of the millsuction to diaphragm and allow spring to move suction switch contact 29downwardly into engagement with cooperating points 55. This completesfor alarm switch AS an energizing circuit shown as extending from powersource conductor 36 through suction switch contacts 29 and 55, conductor56 and the winding of relay AS to power source conductor 37.

The resultant energization starts pick up of AS switch contact 48 and ifthe feed tube plugging persists for the full delay period set byadjuster 50, contact 48 will engage point 49 and connect alarm circuit46 with power source 3637, thereby indicating (as through devices 5253)that some corrective action should be taken. Such corrective action mayconsist in shutting down of the mill long enough to clear the feed tube8 of the plugged material.

Once the feed tube 8 has been reopened, resumption of normal operationof the mill is accompanied by communication of the mill suction todiaphragm 25 which opens the contacts of suction switch 29 and therebydeenergizes alarm switch AS. Contact 48 of said switch now promptlyreturns to the released position shown. If the duration of the feed pipeplugging is less than the pick up time of a 4\ v switch AS, contact 48will have moved only partly up when suction switch 29 deenergizes thewinding of switch AS; and that contact 48 of said switch then willquickly drop back to its fully released position without havingactivated the alarm circuit 4546.

Cooperation with flow indicator for mill feeder Another aspect of thisinvention resides in novelly utilizing the suction-alarm facilities justdescribed in conjunction with no-flow alarm apparatus provided for themill feeder 10. One form of mill alarm apparatus satisfactory for thispurpose is the microphone-amplifier arrangement disclosed and claimed bya copending application Serial No. 158,212, filed April 26, 1950, nowPatent No. 2,659,881, in the names of Alexander Bogot and Harry A.Bishop for Detection of Stoppage in the Flow of Divided Material.

In the scheme of that copending application there is inserted throughone of the walls of feeder 10s casing a flow-detector member 18 hereshown in the form of a small diameter (as A) round stainless steel rodprojected as indicated into the downward flow path of the coal releasedfrom hopper 22 by star wheel 23 into the central feed tube 8 of thepulverizing mill. The rod mounting is made cushioned or yieldable (asthrough employment of a sponge rubber disc 21 covering an enlargedopening in the casing wall and snugly supporting the rod at its center)in order that individual lumps of the fuel in contacting the rod 18 canset up therein vibrations which accompany the normal flow of fuel butwhich cease Whenever that flow is stopped.

Attached to the outer projecting end of this detector rod 18 is amicrophone 32 which translates into electrical impulses the aforesaidmechanical vibrations which the flowing fuel sets up in the detector.Such electrical impulses are communicated by conductors 38 to anamplifier 34 wherein they are strengthened and otherwise made suitablefor accomplishing desired control functions. This amplifier may utilizeelectronic tubes conventionally organized (and hence not representedhere) and is shown as being powered from the energizing source 3637earlier mentioned.

From the amplifier the strengthened impulses pass into rectifier andfilter apparatus 35 which converts them into a signal current that isimpressed upon the winding of a fiow responsive relay FR via conductors39. This signal current continues to persist only as long as flowingfuel from feeder star wheel 23 continues to hit detector member 18 andset up therein the aforesaid vibrations which microphone 32 convertsinto electrical impulses that when appropriately strengthened byamplifier 34 are applied to rectifier and filter apparatus 35.

The named relay FR energized by the resulting signal current is providedwith a contact 40 which is held open by that current during theaforesaid conditions of normal fuel flow into the top 8b of mill feedtube 8. However, when that fuel flow stops and said signal currentceases to flow through the FR relay winding, contact 41 is allowed todrop into engagement with point 41. In the combination system hereshown, such engagement duplicates the action of suction switch 29 inconnecting the winding of alarm switch AS with energizing source 36-37;as later description herein will make more fully evident.

Relay FR is safeguarded against false signal current energization whenno falling fuel hits detector member 18 and when said member is thussubjected only to the vibrations set up by the feeder 1'0 and theassociated pulverizing mill during operation thereof; this safeguardtaking the form of a sensitivity adjuster 43 for the amplifier 34. Ineach installation this control 43 is set by trial and error so that milland feeder vibrations alone cannot activate flow responsive relay FR;such setting once made assuring that said relay FR will respond indesired manner only to actual flow of fuel downwardly from feeder 10into the mill feed tube 8.

How the combination alarm system operates From the drawing Fig. 1 itwill be seen that the alarm circuit 45-46 is normally inactive and is sokeptas long as the flow relay FR is he d picked up (by actual passage offuel into the top of mill feed tube 8) and the suction switch 29 is heldopen (by transmission of the mill suction to diaphragm 25 through feedtube 8).

Should there be a stoppage in the flow of fuel downwardly past detector18 and into feed tube 8, then flow responsive relay FR will releasecontact 18 to energize alarm switch AS and thereby activate the alarmcircuit -46 if the stoppage persists for a time longer than the AS pickup delay for which adjuster is set. In this event an appropriate alarmwill be given in the manner already explained.

Moreover, should the mill feed tube 8 become clogged with fuel orotherwise stopped up, the resultant loss of suction to diaphragm 25 willallow closure of suction switch 29 and thereby also activate the alarmcircuit 4546 if the clogging persists for a time longer than the AS pickup delay. Under this further condition an appropriate alarm likewisewill be given by devices 5253.

'lhe advantage of this combined arrangement is that cloggings in themill feed tube 8 at any point below the location of detector member 18are directly indicated by suction switch 29, whereas if such switch werenot provided there could be no indication of the clogging until the fuelhad backed completely up to the level of detector 18. Such packing offuel in a substantial length of this feed tube 8 is highly undesirablein that clearing of the tube when so fully packed is a major operationmuch more diflicult to perform than when the clogging is allowed tobuild up through only a short length.

When so novelly used in conjunction with the microphone detector 18, thesuction-switch facilities of this invention thus perform a function ofpractical significance and commercial importance; it being apparent thatwhen pulverizing mills are constructed as shown in the drawing hereof itbecomes physically impractical to install a microphone detector 18 closeto the lower end 8a of mill feed tube 8 (as within the confines of millcasing 3 or top olftake 19) But the suction-responsive facilities heredisclosed do provide for this portion of the feed tube and they thusconstitute a valuable adjunct to the microphoneamplifier facilities ofcopending Bogot-Bishop application Serial No. 158,212.

Alternative arrangement of Fig. 2

In the organization of Fig. 1 relay AS functions to introduce a timedelay between each closure of suction switch 29 and each resultantactivation of alarm circuit 4546.

In certain situations it may be desirable that such time delay beeliminated; thereby assuring a correspondingly earlier giving of analarm in response to clogging of fuel feed tube 8. Such elimination maybe accomplished by modifying the Fig. 1 circuits in the mannerrepresented by Fig. 2; the referred to modification res 1ding inshifting the conductor 56 connection (with suction switch 29) from thewinding of alarm switch AS (Fig. l) to the alarm circuit conductor 46 asshown at 56 in Fi 2.

Nith the circuits so modified (Fig. 2), closure of suction switch 29 nowdirectly activates alarm circuit 4546 (without any time delay) byconnecting the one alarm conductor 46 with the first power sourceconductor 36 over conductor 56' and suction switch contacts 29 and (theother alarm conductor 45 being continuously oined with the second powersource conductor 37 in both Figs. 1 and 2 In this way (Fig. 2) responseof the alarm devices 52-53 to plugging of fuel feed tube 8 can becorrespondingly quickened, because the delayed action alarm switch AS isno longer utilized (as in Fig. 1) in giving alarms initiated by thesuction switch 29.

What is claimed is:

1. In a system of the type described the combination of a pulverizingmill, a feed tube for conveying material to be pulverized into theinterior of said 1111, means for maintaining said mill interior and thedischarge end of said feed tube under suction, a feeder for dispensingsaid material into the inlet end of said feed tube while sealing saidtube end against admission of air, a suctionresponsive device connectedwith the inlet end portion of said feed tube for reception of theaforesaid mill suction as transmitted from the mill interior through theteed tube, a switch actuated by said suction-responsive device, andnormally-inactive alarm means controlled by said switch and renderedactive thereby if transmission of the mill suction to said device ceasesas in response to a clogging of the feed tube.

2. The combination with a pulverizing mill of a feed tube for conveyingmaterial to be pulverized into the interior of the mill, means formaintaining said mill interior and the discharge end of said feed tubeunder suction, a feeder for dispensing said material into the inlet endof said feed tube while sealing said tube end against admission of air,a suction-responsive device connected with the inlet end portion of saidfeed tube for reception of the aforesaid mill suction as transmittedfrom the mill interior through the feed tube, a quickacting switchactuated by said suction-responsive device, and a delayed-response relaycontrolled by said switch and disposed to occupy an inactive position aslong as said suction transmission through the feed tube continues but togo to an alarm position when said transmission ceases as in response toa clogging of the feed tube.

3. In a system of the type described the combination of a pulverizingmill, a feed tube for conveying material to be pulverized into theinterior of said mill, means for maintaining said mill interior and thedischarge end of said feed tube under suction, a feeder for dispensingsaid material into the inlet end of said feed tube while sealing saidtube end against admission of air, a suction-responsive device connectedwith the inlet end portion of said feed tube for reception of theaforesaid mill suction as transmitted from the mill interior through thefeed tube, a switch actuated by said suction-responsive device, an alarmrelay controlled by said switch and disposed to occupy an inactiveposition as long as said suction transmission through the feed tubecontinues but to go to an alarm position in time-delayed response todiscontinuance of said transmission, and an alarm circuit activated bysaid relay when in said alarm position as by reason of prolongedclogging of the feed tube.

4 The combination with a pulverizing mill of a feed tube for conveyingmaterial to be pulverized into the interior of the mill, means formaintaining said mill interior and the discharge end of said feed tubeunder suction, a feeder for dispensing said material into the inlet endof said feed tube while sealing said tube end against admission of air,a suction-responsive device connected with the inlet end portion of saidfeed tube for reception of the aforesaid mill suction as transmittedfrom the mill interior through the feed tube, normallyinactive alarmmeans controlled by said suction-responsive device and rendered activethereby if said transmission of the mill suction to the device ceases asis response to a clogging of the feed tube, a detector member responsiveto flow of the aforesaid material dispensed by said feeder into saidfeed tube, and relay means controlled by said detector member anddisposed also to render the aforesaid alarm means active if the flow ofsaid material from the feeder into the mill feed tube is discontinued.

References Cited in the file of this patent UNITED STATES PATENTS1,892,790 S melser Ian. 3, 1933 2,235,928 Hardinge Mar. 25, 19412,494,124 Hegy Jan. 10, 1950

